362 W. G. Van Name — Bermuda 'Ascidians. 



Genus Leptoclinum Milne-Edwards, 1841. 



Differs from Didemnum in having four rows of stigmata, and in 

 forming a thin incrusting colony, densely crowded with calcareous 

 spicules, so that the test becomes more or less hard and brittle. 



Some species are said to have an atrial languet, but probably these 

 should be placed in another genus. 



In some cases the testis is deeply lobed, or it may be completely 

 divided into two glands. 



This genus is none too well distinguished from Didemnum, but is 

 accepted by nearly all writers. The number of rows of stigmata 

 (though apparently a reliable character in the Bermuda forms) is by 

 no means always invariable, even in the same species, and in the 

 character of the colony every gradation is found between the mas- 

 sive colony of a tj^pical Didemnum and the thin, brittle crust of a 

 typical Leptoclinum. 



In this paper the writer has placed all the forms with three rows 

 of stigmata in Didemnum, regardless of the thickness of the colony. 



True Leptoclinums, with four rows of stigmata, occur in abund- 

 ance at Bermuda, growing on corals, sponges and algae on the 

 reefs, and on the under side of stones along the shore, up to a point 

 well above low-water mark. It is the most abundantly represented 

 genus of ascidians there. 



With only a limited number of specimens at hand, it is easy to 

 classify them into several distinct and well marked species, differing 

 from each other fully as much as some of the forms which are 

 described above as species of the genus Didemnum, but with a large 

 number of specimens available for study, the problem is by no means 

 such an easy one, as so many intermediate forms occur. The writer 

 devoted particular attention to collecting examples of this genus 

 during his visit to Bermuda in 1901, but is obliged to confess, after 

 examining a very large amount of material, that he has utterly failed 

 to discover any character or characters by which the Bermuda 

 Leptoclinums may be divided into groups worthy of specific rank. 

 Apparently a process of active evolution is going on in the members 

 of this group, at least in the Bermuda representatives of it, and 

 from the hopeless confusion in which the species of this genus gen- 

 erally are involved, it seems not unlikely that this is the case else- 

 where as well. 



As the differences between the varieties are too great to disregard 

 entirely, the only course open to the writer is to describe the most 



